Traditionally, road pavement stripes were applied to road surfaces by spraying paint onto the road surface from specially equipped trucks. A number of problems are associated with painted pavement stripes. One problem is the tendency for paint to rapidly wear off due to the effects of vehicular traffic and weather conditions. Another problem is the poor reflectivity of painted stripes, particularly in fog or other low light conditions.
In response to these problems, specialized striping tapes have been developed to replace painted pavement stripes. These tapes, such as that sold under the Stamark.TM. name by the 3M Corporation, provide a dual benefit of greater reflectivity and greater resistance to elements. These marking tapes are typically on the order of about 60 mils in thickness, which thickness itself is both a benefit and a detriment. The benefit of the increased depth of the tape as compared to paint allows for much longer wear and durability. However, a problem occurs with the tape, especially when used on road surfaces in northern climates, in that snow plows tend to scrape the tape away along with the snow. Since the marking tape is considerably more expensive than painted stripes, the cost of replacing the tape after damage by snow plows has limited or prohibited its use in many regions.
Recently, experiments have been conducted with grooving the pavement before installation of the tape. Grooves of a depth somewhat less than the tape depth, e.g. on the order of 40 mils in depth, are cut into a concrete and asphalt pavement surface and the tape is then adhesively applied into the grooves. This has proven to be such an improved method of pavement marking tape installation that some states are mandating this type of application when marking tape is used. For example, the State of Kansas Department of Transportation (and the 3M Corporation) specify a groove depth for the application of pavement marking tape of 40 mil .+-.10 mil. This degree of precision has been impossible to achieve with existing concrete and asphalt slot cutting equipment. This is because existing equipment, such as that shown and described in U.S. Pat. No. 4,797,025 to Kennedy, is designed with blades which are directly attached to a propelling unit such that the unit is propelled forward while the cutting blades are lowered into the pavement to a predetermined depth. Due to the lengthy wheel base of the propelling unit and the rigid connection between the propelling unit and the blades, when the pavement surface has irregularities, such as high spots, the cutting blades will cut too deeply into the pavement, thus exceeding the specified slot depth. Conversely, when depressions occur in the pavement, the cutting blades will be raised to a point such that slots are too shallow. In extreme dips in the pavement surface, the cutting blades can actually skip out of the pavement, leaving gaps in the slots.
It is clear then, that a need exists for a concrete and asphalt slot cutting machine which can cut slots of a precise depth into road pavement regardless of irregularities in the pavement surface. Such a machine should be reliable and durable yet simple to operate.